The changing shape of the U.S. population age structure will dramatically increase the number of osteoporotic fractures in the elderly;the increase will disproportionately affect minorities and men. It is therefore important to understand the epidemiology of osteoporosis in these populations. While there are clear racial/ethnic differences in fracture rates, their origins are not understood. The proposed study will be a comprehensive effort to further our understanding of the fundamental causes of racial/ethnic disparities in fracture rates by focusing on markers of two primary `upstream'determinants of fracture: falls and bone fragility. The Boston Area Community Health/Bone (BACH/Bone) Survey is a study of skeletal health in a randomly selected group of 1,219 black, Hispanic, and white men between 29-80 y. BACH/Bone staff have been very productive, producing over 10 papers for peer-reviewed journals. We propose a second wave of data collection on ~825 men to begin ~6.5 y after baseline, when the cohort will be between 35-86 y. The Specific Aims of the proposed study are to, in a racially/ethnically diverse, population-based sample of men: 1) Estimate longitudinal changes in markers of bone strength and fall risk, with and without adjustment for known risk factors;2) Determine the relative contributions of social factors, individual risk behaviors and health status, and physiological influences to racial/ethnic differences in markers of fall risk and bone strength;3) Establish the first age- and racial/ethnic group-specific, population-based estimates of bone microarchitecture, and identify determinants of observed age and racial/ethnic differences;4) Determine whether there are age and racial/ethnic differences in the ratio of bone loads to bone strength (the `factor of risk');5) Examine whether genetic ancestry contributes to variations in markers of fall risk and bone strength beyond that attributable to self-identified race/ethnicity. The representativeness and racial/ethnic diversity of the BACH/Bone cohort are unique, and, as such, the potential impact of the study is enormous. By focusing upstream on markers of fall risk and bone strength with state-of-the-art measures, it will make landmark contributions to our understanding of the elusive mechanisms underlying racial/ethnic differences in bone fragility. PUBLIC HEALTH RELEVANCE: The Boston Area Community Health/Bone Survey is an observational research study examining the complex relationships between aging, social structure, health and lifestyle, hormones, genetic factors, and markers of fall risk as well as bone strength in a population-based sample of racially/ethnically diverse aging men. Findings will continue to inform our understanding of bone fragility, bone loss, and osteoporosis.